Composite material

ABSTRACT

A composite material has a base substrate body with first and second coatings. Each coating is formed by a multiphase layer of titanium oxide and at least two oxides from the group of aluminum, zirconium, and hafnium oxide and a second single-phase layer on the first layer consisting of only one oxide of aluminum, zirconium, and hafnium.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of PCT applicationPCT/DE2003/003228 filed 26 September 2003 with a claim to the priorityof German patent application 1024665.1 itself filed 7 Oct. 2002 andGerman patent application 10251404.6 itself filed 5 Nov. 2002.

FIELD OF THE INVENTION

The invention relates to a composite material of a base body with amulti-layer coating. Such composite bodies are, for example, used ascutting inserts for machining purposes, namely, turning, milling orboring. The base bodies, to which the coating can be applied by physicalor chemical vapor deposition processes. (PVD or CVD), can be composed ofhard metal, a cermet, steel or a ceramic.

BACKGROUND OF THE INVENTION

DE 27 36 982 A1 already describes a wear resistant coating for shapedparts, especially for tools, comprised of a shaped body, preferably ofhard metal, and one or more surface coatings, at least one of which is aprotective layer with a ceramic matrix into which a further material isincorporated. The ceramic matrix and the material incorporated thereinhave different coefficients of thermal expansion so that the protectivelayer is subject to the formation of fine microcracks therein.Unstabilized and/or partially stabilized ZrO2 has been proposed as thematerial incorporated into the interstices of a ceramic matrix of Al₂O₃.To produce such a layer by the CVD process, AlCl₃, CO₂ and H₂ areadmitted as a gas phase into a reaction vessel at 1100° C. to produceAl₂O₃ or ZrCl₄ and water vapor (H₂O) are admitted to produce ZrO₂.Because of the density difference between the tetragonal modification ofZrO₂ formed at temperatures above the transformation temperature ofabout 1100° C. and the monoclinic modification formed below about 1100°C., with a corresponding phase conversion there can be a significantchange in volume of the deposited ZrO₂. As a consequence, withincreasing volume proportions of the ZrO₂ there is a simultaneousincrease in the microcrack density in the deposited ceramic layer.

In DE 28 25 009 C2 (U.S. U.S. Pat. No. 4,180,400), a hard metal bodywith a thin wear-resistant surface layer of Al₂O₃ has been described andwhich is composed completely or at least 85% of the κ-modification andany possible remainder of the α-modification, forming surface regions orpatches at most 10 μm in size. The aluminum oxide layer can containfurther additions of titanium, zirconium and/or hafnium. To create thisceramic layer by the CVD process, the gas mixture apart from AlC₃, CO₂,CO and H₂ has also small amounts of 0.03 to 0.5% TiCl₄ added to it. Thisaddition, however, serves exclusively or nearly exclusively for theformation of the κ-Al₂O₃ phase.

A further CVD process for depositing Al₂O₃ and/or ZrO₂ using additionalreagents, like hydrogen sulfide, has been described in EP 0 523 021 B1(U.S. Pat. No. 5,674,564).

DE 195 18 927 A1 (U.S. Pat. No. 5,827,570) describes a coated cuttingtool comprised of a substrate of sintered carbide or ceramic with awear-resistant composite ceramic coating which has two different metaloxide phases, for example of Al₂O₃ and ZrO₂ and in addition thereto adoping agent selected from the group of sulfur, selenium, tellurium,phosphorus, arsenic, antimony, bismuth or compounds of these elements.To produce this two-phase layer by a CVD process, for example AlCl₃ andZrCl₄, CO₂ with H₂ as a carrier gas, in addition to an H₂S gas, ispassed over the substrate body at a temperature of about 700° to 1250°C. and a pressure from 133 Pa to ambient pressure, whereby the two-phaselayer with the doping agent is deposited.

EP 0 786 536 A1 (U.S. Pat. No. 5,985,427) describes a coated hard metalbody with a 3 to 30 μm thick aluminum oxide coating which has beendeposited by means of CVD and/or PVD and contains 0.005 to 0.5 weight %chlorine. Optionally 0.5 to 10 weight % Zr and/or Hf and 1.5 to 15weight % Ti can be contained in this coating.

EP 0 162 656 A2 (U.S. Pat. No. 4,746,563) describes a multilayer coatingon a hard metal substrate body which is comprised of an inner layer,which is composed of at least one carbide, nitride, carbonitride,carbo-oxygen nitride, oxynitride, boron nitride or boron-carbonitride oftitanium, and an outer multilayer coating with a total thickness of 5 to20 μm and provided with an outer layer of a plurality of Al₂O₃ coatingswith a respective thickness of 0.01 to 2 μm and each comprised of anAl₂O₃ film in which titanium oxide has been dissolved or which has beencodeposited with at least 30 volume percent titanium oxide. The layersare separated by intervening layers with respective thicknesses of 0.01to 2 μm and which each can comprise TiC, TiN, TiCN, TiCNO, TiNO,titanium oxides, Ti(B,N), Ti(B,N,C), SiC, AlN or AlON.

In WO 00/17 416 (U.S. Pat. No. 6,660,371), a composite material of acoated hard metal or cermet base body has been described on which thesingle layer or a multilayer coating is applied at least in the form ofa 0.5 μm to 25 μm thick coating and preferably the outermost phase is anAl₂O₃ phase containing a ZrO₂ and/or HfO₂ phase which in turn contains athird fine dispersive phase consisting of an oxide, oxycarbide,oxynitride or oxycarbonitride of titanium. The proportion of the thirdphase in the overall composition of this layer amounts to 0.2 to 5 mol%. To produce such a three phase layer, a CVD process with depositiontemperatures between 900° C. and 1000° C. is selected in which the gasesrequired for the deposit contain chlorides of the Al, Zr and Hf, and inaddition CO₂, H₂, CH₄ and N₂ or inert gas under pressures of 10 to100,000 Pa. The TiO_(x) incorporated as the third phase has a positiveeffect on the growth speed and on the particle sizes of the aluminumoxide and zirconium or hafnium oxide. Preferably a coating temperatureof 960° C. is selected in which the ZrO₂ is present in the monoclinicform. From the mentioned publication, therefore, hard metal substratebodies are known which have layer sequences TiN—Ti(C,N) and thedescribed three phase layer.

OBJECT OF THE INVENTION

It is the object of the present invention to provide a composite bodywhich, when used as a cutting insert, affords increased cuttingaffectivity as well as a longer useful life. Higher cuttingeffectiveness is determined in terms of the desired high cutting speedsand increased thicknesses of the chip removed. If possible such cuttinginserts should be usable in so-called dry cutting operations.

SUMMARY OF THE INVENTION

These objects are attained with a composite material having a base bodycarrying at least one multiphase coating of the oxides of aluminum,zirconium and/or hafnium and of titanium (as a three phase coating) anda single-phase layer or coating of Al₂O₃, ZrO₂ or HfO₂. In the coatingon the base body, therefore, there is, both at least one mutiphase oxidelayer as well as at least one single-phase oxide layer. The multiphaselayer can, apart from the three-mentioned oxide components, contain MgOand the single-phase layer can additionally contain up to 1% of atitanium oxide proportion. According to a further feature of theinvention, however, at least two and preferably at least three layersare, provided of which each is comprised of the mentioned multiphaselayer of the oxides of Al, Zr, Ti and/or Al, Hf, Ti and/or Al, Zr, Ti,Mg and/or Al, Hf, Ti, Mg, and a single-phase oxide layer of an oxide ofHf, Zr or Al. Preferably at least three-phase or four-phase oxide layersare provided between which respective single-phase oxide layers aredisposed and whereby a single-phase oxide layer also forms the outercover coating. These layers have a fine grained lattice structure and auniform phase distribution and provide a high degree of thermalinsulation. The base body can also be comprised of a hard metal, acermet, or steel or a ceramic material.

Between the substrate body and the first oxide layer which preferably isa multiphase oxide layer is at least one layer of a carbonitride oftitanium, hafnium, zirconium. This cover layer can have a thicknessbetween 2 to 15 μm, especially 3 to 8 mm.

According to a further feature of the invention it is possible toprovide, between the multiphase oxide layer and the single-phase oxidelayer, preferably in a multi layer sequence of the multiphase oxidelayers and single-phase oxide layers between each of the mentionedlayers, one or more intermediate layers of titanium, hafnium orzirconium carbonitride.

These intervening layers have preferably a thickness between 0.2 and 3μm, especially of 2 μm.

The total thickness of all multiphase oxide layers and all single-phaseoxide layers preferably lies between 6 and 20 μm especially at 10 μm.The difference of a single-phase oxide layer can amount to 2 to 6 μmpreferably 4 μm and the thickness of an individual single-phase oxidelayer can amount to 1 to 5 μm preferably 3 μm.

The multiphase coating is produced by a CVD process which is basicallyknown from WO 00/17 416 or as the so-called middle temperature. CVDprocess.

In a further embodiment of the invention, to eliminate tensile stressesor to increase compressive stresses in the composite body, the compositebody can be subjected to a treatment with a blasting agent, the blastingagent being preferably composed composed of a hard metal granulate whichcan have a substantially rounded grain configuration and a maximum graindiameter of 200 μm and more preferably of a maximum of 100 μm.

BRIEF DESCRIPTION OF THE DRAWING

Further advantages of the invention are described in connection with anexemplary embodiment. The drawing shows.

FIGS. 1 to 3 respective diagrams which provide information with respectto the improved life of the composite material according to theinvention in cutting inserts by comparison with the state of the art.

SPECIFIC DESCRIPTION

The test objects were in all three cases cutting inserts of the typeCNMG120412-5. In all three cases the substrate: body:

was a hard metal (THM) but the coatings were different in the threecases. In a first test series the work press was gray cast iron with acutting speed of 450 m/min and a cutting depth of: 2. 5 mm and anadvance of the cutting insert of 0.315 mm per revolution. The firstcutting body was comprised of a hard metal base body coated with a twolayer coating of TiCN—Al₂O₃ (as an outer layer). The life achieved wasless than 2 min. A significantly improved life was given with a twolayer coating in which on a TiCN— cover layer a three phase oxide layeraccording to WO 00/17 416 was applied comprised of Al₂O₃/ZrO₂/TiO_(x).

A clear improvement in the useful life still further can however beachieved with a cutting insert which had a TiCN adjacent the substratebody and a six layer outer coating which was comprised of threeindividual layers each of a three phase oxide coating and a single-phaseZrO₂ layer.

In a second test a gray cast iron workpiece with an extremely roughsurface is machined by turning whereby in comparison to the previouslydescribed test only the cutting speed was reduced to 200 m/min. Basedupon this cutting speed, there was obtained a useful life of 6 min forthe cutting inserts with a TiCN—Al₂O₃ coating, of about 7 min forcutting inserts with a TiCN—Al₂O₃/ZrO₂/TiO_(x) coating, and a usefullife of 9 min for a cutting insert with the coating of the invention inwhich by contrast with the previously described versions had a threetimes alteration of a three-phase oxide layer of Al₂O₃/HfO₂/TiO_(x) andthe single-phase oxide layer of HfO₂. The above described cutting testswere carried out with so-called dry cutting.

As FIG. 3 shows, however, with use of a lubricant coolant, still higheruseful lives can be obtained. In the lathe turning of is grey cast ironat cutting speeds of 450 m/min, a cutting depth of 2.5 mm, and a feed of0.315 mm per revolution, the useful life of the cutting insert with aTiCN—Al₂O₃ cutting amounted to about 4.5, min, the useful life of acutting insert with a coating according to WO 00/17 416 was about 6.5min, whereas the coating according to the invention resulted in usefullives of 10 or 12.5 min. Especially when HfO₂ forms the single-phaseoxide layers, it is possible to obtain a still more substantial increasein the useful life by comparison with the already improved life usingZrO₂ as the single-phase oxide layer. All coatings were applied by theso-called CVD-MT (middle temperature) process under the same processconditions.

1. A composite material comprised of: a base substrate body; a firstcoating on the base body of a multiphase layer of titanium oxide and atleast two oxides from the group of aluminum, zirconium, and hafniumoxide and a second single-phase layer on the first layer consisting ofonly one oxide of aluminum, zirconium, and hafnium; and a second coatingon the first coating of a multiphase layer of titanium oxide and atleast two oxides from the group of aluminum, zirconium, and hafniumoxide and a second single-phase layer on the respective first layerconsisting of only one oxide of aluminum, zirconium, and hafnium.
 2. Acomposite material according to claim 1 wherein each multiphase layercontains an additional proportion of MgO or each single phase layercontains up to 1% of an additional titanium oxide.
 3. The compositematerial according to claim 1 wherein the base body is composed of ahard metal, steel, cermet or ceramic.
 4. The composite materialaccording to claim 1 wherein between the substrate body and the firstmultiphase oxide layer, at least one layer of TiCN, HfCN or ZrCN isprovided which has a thickness of 1 to 15 μm.
 5. The composite materialaccording to claim 1 wherein between each multiphase oxide layer and therespective single-phase oxide layer, one or more intermediate layers areprovided of TiCN, HfCN, or ZrCN, each of which has a thickness between0.2 μm to 3 μm.
 6. The composite material according to claim 1 whereinthe total thickness of all of the multiphase oxide layers and all singlephase oxide layers is 6 to 20 μm, the thickness of an individualmultiphase oxide layer being 2 to 6 μm, or the thickness of theindividual single phase oxide layer being 1 to 5 μm.
 7. The compositematerial according to claim 1 wherein the multilayer coating is producedby means of CVD.
 8. The composite material according to claim 1 whereinthe composite material is subjected to a final dry blast treatment usinga granular blast agent composed of a high metal granulate and which atleast in major part has a rounded grain configuration with a maximumdiameter of 150 μm.
 9. The composite material defined in claim 1,further comprising: a third coating on the second coating of amultiphase layer of titanium oxide and at least two oxides from thegroup of aluminum, zirconium, and hafnium oxide and a secondsingle-phase layer on the respective first layer consisting of only oneoxide of aluminum, zirconium, and hafnium.